1. Field of the Invention
The present invention relates to machine tool having a door, and in particular, machine tool having a door of which the opening and closing speeds can be changed.
2. Description of the Related Art
An increase in the opening and closing speeds of the door provided in machine tool can shorten the period of time for changing a work, which then shortens the process cycle, and thus leads to an increase in productivity. Therefore, servo driven automatic doors that can be opened and closed at a high speed have been proposed.
Japanese Unexamined Patent Publication 2014-205231 discloses a machining system that is provided with a machine tool having a door that is closed at the time of machining and that is open when nothing is being machined, an automatic changing device that automatically changes an object to be machined and is provided so as to be able to go inside the machine tool or leave the inside of the machine tool via the door, and an actuator for opening and closing the door so that the opening and closing operations of the door can be carried out over a short period of time.
Japanese Unexamined Patent Publication 2002-349133 discloses a mechanism that mechanically separates the door from the driving source when a load of a certain level or higher is applied to the door in order to increase the level of safety when an operator touches the door.
Japanese Unexamined Patent Publication H5 (1993)-123937 discloses a technology for cutting off the power supply to the motor for the opening and closing operations of a front door in a machine tool where the front door is provided in the machine body cover when it is detected that the door of the machine body cover is open in order to secure the safety when a tool exchanging operation is carried out by opening the front door.
Japanese Unexamined Patent Publication H8 (1996)-85037 discloses a technology for allowing an override control device to change the override value to a predetermined value which is outputted to the control unit of a machine tool upon the reception of a door open signal from a door opening and closing sensor during the operation of the machine tool, and for allowing the control unit of the machine tool to stop or reduce the speed of the operation of the machine tool in accordance with the override value that has been changed.
Japanese Unexamined Patent Publication 2008-207270 discloses a technology for safely stopping a door when the door collides with an obstacle in order to prevent an external force from being applied to the two, and thus prevent the two from being damaged.
Japanese Unexamined Patent Publication 2002-4715 discloses a technology for reducing the frequency in which the door unit opens and closes when the amount of traffic is high in order to increase the level of safety of the passengers and in order to improve the durability of the automatic door.
Japanese Unexamined Patent Publication 2001-304948 and Japanese Unexamined Patent Publication 2010-211467 disclose a technology for calculating the weight of a moveable unit from the torque of the drive unit and the actual acceleration of the moveable unit.
Japanese Unexamined Patent Publication H3 (1991)-256692 discloses a technology for the emergency stop of a machine within a safety fence when the fence is opened.
Automatic doors that open and close at a high speed could be a source that is dangerous for an operator, and therefore, it is necessary for an operator to secure the safety when the operator touches the door in the case where the operator needs to approach the door in order to give instructions to a robot or to maintain the machine.
In accordance with the technology disclosed in Japanese Unexamined Patent Publication 2014-205231, however, the door provided in machine tool is opened and closed by driving a servo motor so that the opening and closing speeds of the door can be controlled, and the disclosed technology does not relate to the safety when an operator touches the door.
In the mechanism disclosed in Japanese Unexamined Patent Publication 2002-349133, such a problem arises that the mechanism operates due to the inertial force when the acceleration or the deceleration of the door is increased. It is desirable to increase the acceleration or the deceleration in order to shorten the period of time when the door opens and closes, and therefore, the above-described mechanism is not appropriate for doors that open and close at a high speed.
Japanese Unexamined Patent Publication H5 (1993)-123937 and Japanese Unexamined Patent Publication H8 (1996)-85037 disclose technologies for stopping or reducing the speed of the mechanism inside machine tool in the case where the door of the machinery opens, which are not technologies for the safety measures of a door that could be a source of danger to an operator.
Japanese Unexamined Patent Publication 2008-207270 discloses a technology for stopping a door in the case where the door collides with an obstacle, but does not state the selection of an appropriate speed.
Japanese Unexamined Patent Publication 2002-4715 discloses a technology for a door of which the opening and closing speeds can be changed, but the technology relates to the control for opening and closing a door in the door unit having a large amount of traffic, and thus, the technology does not relate to a door of machine tool, and a method for determining appropriate opening and closing speeds is not disclosed.
Japanese Unexamined Patent Publication 2001-304948 and Japanese Unexamined Patent Publication 2010-211467 do not disclose a technology relating to the control for opening and closing a door.
In Japanese Unexamined Patent Publication H3 (1991)-256692, the machine within a safety fence makes an emergency stop when the fence is opened, but the sudden stop could cause damage to the machine. In addition, there is a problem that the recovery from the state of an emergency stop takes time.